1. Technical Field
The present invention relates to a process for producing oil from a subterranean hydrocarbon-bearing formation, and more particularly to such a process wherein a polymer enhanced foam is placed in the formation to reduce gas production therefrom due to gas override or gas channeling, thus sustaining or increasing the oil production rate from the formation.
2. Description of Related Art
Oil production wellbores in formations undergoing gas flooding or other gas injection operations can become uneconomic due to excessive gas production from the wellbore. Such undesirable gas production can result from gas gravity override or gravity-driven gas channeling high in the producing interval.
Gas gravity override is the tendency of injected gas to gravity segregate and propagate excessively quickly in the upper portion of a producing interval, i.e., high up in the interval, due to the low density and high mobility (low viscosity) of the injected gas. Gravity-driven gas channeling is an excessively high propagation rate of injected gas in the upper portion of a producing interval due specifically to the presence of high-permeability heterogeneities therein, whereas gas gravity override often occurs in producing intervals made up solely of homogeneous matrix. Although it may be desirable at some point in an oil recovery process to recover gas injected into a producing interval for such purposes as pressure maintenance, oil mobilization or oil displacement, the above-recited mechanisms often cause the injected gas to prematurely break through to the production wellbore via the upper portion of the producing interval before fully serving its intended purpose.
Consequently, gas gravity override and gravity-driven gas channeling in the upper portion of the producing interval result in detrimental and costly production of gas at the expense of otherwise relatively high rates of more desirable oil production. Gas production due to gas gravity override or gravity-driven gas channeling competes with oil production so that an excessive gas production rate causes a corresponding diminished oil production rate. Thus, every barrel of increased oil production rate resulting from a reduction in gas production represents an incremental barrel of oil production rate and an accelerated cash flow to the producer.
Accordingly, it is an object of the present invention to reduce gas production from an oil production wellbore experiencing gas gravity override or gravity-driven gas channeling. It is another object of the present invention to reduce the gas/oil ratio from an oil production wellbore experiencing gas gravity override or gravity-driven gas channeling. It is also an object of the present invention to increase or sustain the oil production rate from an oil production wellbore experiencing gas gravity override or gravity-driven gas channeling. It is further an object of the present invention to reduce the decline rate of oil production from an oil production wellbore experiencing gas gravity override or gravity-driven gas channeling.